The present invention relates to a method for predicting the resistance to heat deterioration of a sulfur-vulcanized isoprene rubber, more particularly to a prediction method utilizing a solid state nuclear magnetic resonance method employing magic angle spinning by which the resistance to heat deterioration can be predicted with high accuracy.
Heretofore, the resistance to heat deterioration of a sulfur-vulcanized isoprene rubber was evaluated by the ratio of polysulphide in which plural sulfur atoms bridge between polymer chains and monosulphide in which one sulfur atom bridges between polymer chains, obtained through an experiment for example according to swelling compressive method.
As to the heat resistance and heat deterioration, the monosulphide is superior to the polysulphide. Therefore, the resistance to heat deterioration can be estimated roughly from the ratio of the polysulphide and the monosulphide in the rubber.
In the swelling compressive method, the vulcanized rubber is swollen, and the swollen rubber is compressed by applying a load. Then, the measured compressive stress and strain are applied to FLORY's relationship, and the mesh density is obtained as the overall crosslink density.
Further, the rubber is subjected to a chemical treating to cut—S—S— link by the use of lithium aluminum hydride.
The treated rubber is compressed by applying a load, and the measured compressive stress and strain are applied to FLORY's relationship, and the mesh density is obtained as the crosslink density of the monosulphide. Then, by subtracting this density from the overall crosslink density, the crosslink density of the polysulphide is obtained.
In this way, the above-mentioned ratio of the polysulphide and the monosulphide can be obtained as the ratio of the crosslink density of the polysulphide and the crosslink density of the monosulphide.
It is however difficult to accurately evaluate the resistance to heat deterioration from the empirically-obtained ratio of the polysulphide and the monosulphide.